Ice cream or frozen custard machines as well as other systems for cooling or freezing food stuffs, condiments, or other materials, typically include an evaporator situated proximate the material being chilled. For example, in ice cream machines, liquid ice cream is typically inserted in a freezing chamber adjacent the evaporator and is removed from the freezing chamber as solid or semi-solid ice cream. The evaporator removes heat from the freezing chamber as a liquid refrigerant such as FREON.RTM., ammonia, HP62, 502 or other liquid having a low boiling point changes to vapor in response to the heat from the liquid ice cream. Typically, the evaporator is partially filled with vapor as the liquid refrigerant boils (e.g., becomes vapor) in the evaporator.
Since most heat transfer occurs when the liquid refrigerant is changed to vapor, the partially filled evaporator is less efficient than a flooded evaporator (e.g., an evaporator filled entirely with liquid refrigerant). The partially filled evaporator also tends to unevenly cool the ice cream because the parts of the evaporator which are filled with vapor are not able to cool as effectively as the parts of the evaporator filled with liquid. Further, prior art ice cream machines are disadvantageous because the pressure does not remain constant in the evaporator due to the accumulation of vapor. The inefficiencies resulting from the partially filled evaporator require the ice cream machine to use a larger, more expensive, and less energy efficient condenser or pump.
Thus, there is a need for an ice cream machine which utilizes a flooded evaporator. There is also a need for an evaporator which provides even cooling in the freezing chamber.